With growth of a cloud service in recent years, a required information processing amount continues to increase. In order to process a huge amount of data, a data center having enhanced energy efficiency by putting servers and network devices into one place is operated in various areas. However, with increase of an information processing amount in a data center, a power consumption amount in the data center is also increasing.
A data center accommodates electronic devices such as a central processing unit (CPU) and an integrated circuit (Large Scale Integration: LSI). Since these electronic devices involve heat generation, an air conditioner is used to maintain an appropriate temperature inside the data center. However, with increase of an information processing amount, such an air conditioner also requires a huge amount of power.
Accordingly, there is an urgent need to reduce power for an air conditioner in order to cut down on running cost of a data center. As one of attempts to reduce power for an air conditioner, a method is developed whereby heat discharged from a rack, which is a casing for housing an electronic device, is transported to outdoor directly without using an air conditioner, and is radiated to outdoor air. Using such a method makes it possible to reduce air-conditioning power of a data center.
As a method of transporting heat discharged from a rack housing an electronic device to outdoor, a method of using a phase change phenomenon of a coolant is known, besides a method of using a pump to circulate cool water supplied from outside. In this method, a coolant is circulated by constant occurrence of an evaporation phenomenon caused when a coolant undergoes a phase change from a liquid phase to a gas phase, and a condensation phenomenon caused when a coolant undergoes a phase change from a gas phase to a liquid phase. This method of using the phase change phenomenon is characterized by having a large heat transport amount since latent heat of a coolant is used. Thus, this method is expected as a means for reducing power for an air conditioner of a data center.
PTL 1 describes an example of a phase change cooling device that uses a coolant circulation cycle caused by such a phase change phenomenon of a coolant.
A relevant cooling system for an electronic device described in PTL 1 includes an evaporator provided in a vicinity of a server. A cooling coil is provided inside the evaporator, and a liquid coolant flowing through inside the cooling coil deprives surroundings of vaporization heat and gasifies, by being evaporated by hot air generated from the server. The evaporator is provided with a temperature sensor that measures a temperature of air after hot air discharged from the server is cooled by the evaporator. An expansion valve for adjusting a supply flow rate of the coolant to be supplied to the cooling coil is provided at an inlet of the cooling coil. Then, based on a measured temperature by the temperature sensor, a degree of opening of the expansion valve is automatically adjusted.
In addition, return piping and supply piping are connected with the evaporator, and the return piping and the supply piping are provided with a cooling tower and a heat exchanger through on-off valves. Then, a configuration is made such that flow of the coolant is switched by the cooling tower and the heat exchanger, based on a temperature and a humidity of outdoor air.